1. Field of the Invention
This invention relates to an electromagnetic coupler, which is suitable for a wireless communication system for transmitting information using an electrostatic field or an induction electric field between information communication devices placed at a short distance from each other, and an information communication device with the electromagnetic coupler mounted thereon.
2. Description of the Related Art
JP Patent No. 4345851 discloses a conventional electromagnetic coupler. This electromagnetic coupler (high frequency coupler) is constructed by an electrode, a series inductor and a parallel inductor on a board being connected together by a high frequency transmission line. Also, the electromagnetic coupler is disposed in an information communication device such as a transmitter or a receiver. When these transmitter and receiver are arranged so that their respective electromagnetic coupler electrodes face each other, and when the distance between the two electrodes is not more than 2/15 the wavelength λ equivalent to the frequency used, the two electrodes are coupled together by an electrostatic field component of a longitudinal wave component of an electric field, to act as a single capacitance, and integrally as a bandpass filter, therefore allowing efficient information transmission between the two electromagnetic couplers. Also, when the distance between the two electrodes is from 2/15 to 8/15 the wavelength λ equivalent to the frequency used, an induction electric field component of the longitudinal wave component of the electric field is used, thereby allowing the information transmission between the two electromagnetic couplers.
On the other hand, when the distance between the electromagnetic couplers is longer than a constant value, the information transmission therebetween is impossible. This results in the feature that electromagnetic waves produced from the electromagnetic couplers do not interfere with any other wireless communication systems, and that a wireless communication system using the information communication devices equipped with the electromagnetic couplers is not subject to interference from any other wireless communication systems. Because of these features, the wireless communication system using the conventional electromagnetic couplers uses the electrostatic field or the induction electric field of the longitudinal wave at the short distances, and large capacities of data communications between the information communication devices are permitted by a UWB (Ultra Wide Band) communication method using wide band signals.
More specifically, in the electromagnetic coupler disclosed by JP Patent No. 4345851, a through hole formed in a columnar dielectric is filled with a conductor, while an upper end face of the columnar dielectric is formed with a conductor pattern to act as the electrode, and this columnar dielectric is mounted on the printed board formed with a conductor pattern to act as the high frequency transmission line, thereby connecting the high frequency transmission line and the electrode via the conductor in the through hole. The conductor in the through hole is used as an alternative to the above mentioned series inductor, and the high frequency transmission line is connected to a ground pattern via the parallel inductor. The electromagnetic coupler is configured so that information is transmitted therethrough by using the longitudinal wave of the electric field, which develops in a parallel direction to the conductor in the through hole (i.e. to electric current flowing through the conductor in the through hole), when this electromagnetic coupler is fed.
Refer to JP Patent No. 4345851, and JP-A-2006-121315, for example.
Refer also to Misao Haneishi, et al. “SMALL PLANAR ANTENNAS,” The Institute of Electronics, Information and Communication Engineers, pp. 22-23, for example.